The present invention relates to connections for modular orthopaedic implants. More particularly, the present invention relates to a male/female taper connection including a fastener that maintains compression on a male/female taper junction even if the junction settles.
Many orthopaedic implants comprise a body and a stem connectable to the body. The connection between the body and stem is commonly provided by mating tapers on the body and stem. For example, U.S. Pat. No. 5,405,396 teaches a tibial prosthesis comprising a plate and a stem connectable with the plate. The plate includes a female taper and the stem includes a male taper for close fitting within the female taper. In another example, U.S. Pat. No. 3,067,740 ('740) teaches a hip joint prosthesis comprising a socket member, or upper body, and a nail, or stem member. The upper body includes a female taper and the stem includes a male taper for close fitting within the female taper. The upper end of the stem is threaded to receive a cap nut for compressing the upper body and stem into firm engagement. Such prior art tapers can be of a self-locking variety in which case a locking screw or cap nut may be used to reinforce the self-locking feature, or the tapers can be non-self-locking in which case a locking screw or cap nut is necessary to provide locking. One problem with prior taper joints is that the taper can settle after initial assembly, such as when it is loaded by patient activities. The locking screw may then lose compressive contact with the joint and may even begin to unscrew from the implant. The '740 patent teaches the use of a resilient locking plug to prevent the nut from unscrewing by providing a frictional engagement between the threads of the cap nut and the stem. However, this arrangement does nothing to address the loss of compressive contact that would occur during settling. In addition, the use of a resilient material introduces another material into the prosthesis that may be undesirable.